Reference is hereby made to the following, commonly assigned, copending, U.S. Patent Applications which disclose common subject matter: Ser. No. 09/067,729 filed Apr. 28, 1998 for MULTIPLE CHANNEL, SEQUENTIAL, CARDIAC PACING SYSTEMS filed in the names of C. Struble et al.; Ser. No. 09/439,244 filed on event date herewith for MULTI-SITE CARDIAC PACING SYSTEM HAVING CONDITIONAL REFRACTORY PERIOD filed in the names of K. Kleckner et al.; Ser. No. 09/439,565 filed on even date herewith for BI-CHAMBER CARDIAC PACING SYSTEM EMPLOYING UNIPOLAR LEFT HEART CHAMBER LEAD IN COMBINATION WITH BIPOLAR RIGHT HEART CHAMBER LEAD in the names of B. Blow et al.; Ser. No. 09/439,078 filed on even date herewith for MULTI-SITE CARDIAC PACING SYSTEM HAVING TRIGGER PACE WINDOW in the names of C. Juran et al.; Ser. No. 09/439,568 filed on even date herewith for RECHARGE CIRCUITRY FOR MULTI-SITE STIMULATION OF BODY TISSUE filed in the names of B. Blow et al.; and Ser. No. 09/439,243 filed on even date herewith for AV SYNCHRONOUS CARDIAC PACING SYSTEM DELIVERING MULTI-SITE VENTRICULAR PACING TRIGGERED BY A VENTRICULAR SENSE EVENT DURING THE AV DELAY in the names of C. Yerich et al.
The present invention pertains to multi-site cardiac pacing systems for pacing and sensing at first and second spaced apart sites of a patient""s heart in triggered pacing modes in a predetermined sequence, particularly sites in right and left heart chambers.
In diseased hearts having conduction defects and in congestive heart failure (CHF), cardiac depolarizations that naturally occur in one upper or lower heart chamber are not conducted in a timely fashion either within the heart chamber or to the other upper or lower heart chamber. In such cases, the right and left heart chambers do not contract in optimum synchrony with each other, and cardiac output suffers due to the conduction defects. In addition, spontaneous depolarizations of the left atrium or left ventricle occur at ectopic foci in these left heart chambers, and the natural activation sequence is grossly disturbed. In such cases, cardiac output deteriorates because the contractions of the right and left heart chambers are not synchronized sufficiently to eject blood therefrom. Furthermore, significant conduction disturbances between the right and left atria can result in left atrial flutter or fibrillation.
It has been proposed that various conduction disturbances involving both bradycardia and tachycardia of a heart chamber could benefit from pacing pulses applied at multiple electrode sites positioned in or about a single heart chamber or in the right and left heart chambers in synchrony with a depolarization which has been sensed at at least one of the electrode sites. It is believed that cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy and CHF.
A number of proposals have been advanced for providing pacing therapies to alleviate these conditions and restore synchronous depolarization and contraction of a single heart chamber or right and left, upper and lower, heart chambers as described in detail in commonly assigned U.S. Pat. Nos. 5,403,356, 5,797,970 and 5,902,324 and in 5,720,768 and 5,792,203 all incorporated herein by reference. The proposals appearing in U.S. Pat. Nos. 3,937,226, 4,088,140, 4,548,203, 4,458,677, 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259, all incorporated herein by reference. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers is addressed in the ""688 and ""259 patents, as well as in U.S. Pat. Nos. 4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867, also all incorporated herein by reference.
The medical literature also discloses a number of approaches of providing bi-atrial and/or bi-ventricular pacing as set forth in: Daubert et al., xe2x80x9cPermanent Dual Atrium Pacing in Major Intra-atrial Conduction Blocks: A Four Years Experiencexe2x80x9d, PACE (Vol. 16, Part II, NASPE Abstract 141, p.885, April 1993); Daubert et al., xe2x80x9cPermanent Left Ventricular Pacing With Transvenous Leads Inserted Into The Coronary Veinsxe2x80x9d, PACE (Vol. 21, Part II, pp. 239-245, January 1998); Cazeau et al., xe2x80x9cFour Chamber Pacing in Dilated Cardiomyopathyxe2x80x9d, PACE (Vol. 17, Part II, pp. 1974-1979, November 1994); and Daubert et al., xe2x80x9cRenewal of Permanent Left Atrial Pacing via the Coronary Sinusxe2x80x9d, PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April 1992), all incorporated herein by reference.
Problems surface in implementing multi-site pacing in a single heart chamber or in right and left heart chamber pacing within the contexts of conventional timing and control systems. In certain circumstances, it is desirable to deliver a series of pacing pulses at spaced apart sites in a single heart chamber or in the right and left heart chamber pacing pulses as close together in time as possible upon time-out of an escape interval or synchronous AV delay or upon sensing a right or left heart chamber sense event. However, it is not always desirable to do so when pacing pulse amplitudes are programmed differently to provide for an adequate pacing threshold above the pacing amplitude sufficient to capture the heart chamber at a given pulse width. When a pacing system is implanted, the physician undertakes a work-up of the patient to determine the pacing energy and sensing thresholds that are sufficient to capture the heart and to distinguish true P-waves and R-waves from muscle artifacts and ambient electrical noise.
For example, in bi-atrial or bi-ventricular pacing systems, if left atrial pace (LA-PACE) and right atrial pace (RA-PACE) or left ventricular pace (LV-PACE) and right ventricular pace (RV-PACE) pulses are delivered simultaneously, there may be a current contribution from the highest voltage, active electrode delivering the highest voltage pulse to the lower voltage, active electrode delivering the lower voltage pulse. The contribution may be sufficient to lower the pacing threshold at the lowest voltage active electrode. Then, at a later time, the programmed mode may be changed by eliminating or lowering the voltage of the highest voltage pacing pulse, and capture may be lost at the lowest voltage active pacing electrode.
So, in these situations, at least a minimal trigger delay longer than the pacing pulse width of the first pace pulse to be delivered (PACE1) and the second pace pulse (PACE2) is necessary. In addition, the inventors have realized that determining which of the Right Heart Chamber(RHC) sense event or Left Heart Chamber(LHC) sense event has actually occurred and applying PACE1 to the corresponding pace/sense electrode adds unnecessary complexity to the pacing system and method. The inventors have realized that It is desirable and possible to simplify the sequence of delivery of PACE1 and PACE2 pulses in response to a RHC or LHC sense event without sacrificing efficacy of the triggered RHC and LHC pacing.
The inventors have also realized other applications of delivery of time pacing pulses at multiple sites of a patient""s heart in one heart chamber to restore or augment a synchronous depolarization of the heart chamber.
The present invention is therefore directed to delivering at least first and second (or more) pacing pulses to first and second spaced apart sites of the heart in a predetermined sequence in response to a sensed depolarization traversing one of first and second sites, the sequence being fixed or programmed to deliver the first and second pacing pulses independently of which spaced apart site that the sensed depolarization traverses.
The method and apparatus of the present invention contemplates first and second pace/sense electrodes at first and second spaced apart sites of the heart, sensing spontaneous cardiac depolarizations traversing one of the other of the first and second pace/sense electrodes and providing a sense event signal. Upon provision of a sense event signal, a first pacing pulse is delivered to a predetermined one of the first or the second pace/sense electrodes to pace the heart at the site of that pace/sense electrode regardless of whether the sense event signal originates from a spontaneous cardiac depolarization at the first or second spaced apart sites. A triggered pacing delay is commenced and timed out on provision of the sense event signal, and a second pacing pulse is delivered to the other of the first or the second pace/sense electrodes to pace the heart at the site of that pace/sense electrode. A synchronized depolarization of the heart in a predetermined sequence is effected by the first and second pacing pulses.
In RHC and LHC pacing systems and methods of operation, the present invention provides efficient pacing of the RHC and LHC separated by a predetermined triggered delay in a predetermined, programmed or fixed, right-to-left or left-to-right sequence without determining the origin of a RHC or LHC sense event or necessarily employing separate RHC and LHC sense amplifiers.
When separate RHC and LHC sense amplifiers are provided, the present invention provides methods and apparatus for initiating triggered pacing of the RHC and LHC separated by the predetermined triggered delay in the predetermined right-to-left or left-to-right sequence upon either a RHC or LHC sense event.
A single sense amplifier can be coupled to a sense electrode pair situated in relation to the RHC or LHC or traversing the RHC and LHC. In this case, the present invention provides methods and apparatus for initiating triggered pacing of the RHC and LHC separated by the predetermined triggered delay in the predetermined right-to-left or left-to-right sequence upon RHC or LHC or RHC-LHC sense event.
In a bi-chamber pacing system, an IPG optionally having an indifferent IPG can electrode is coupled to a small diameter, unipolar, LHC endocardial lead and a bipolar RHC endocardial lead. The LHC lead is advanced through a venous pathway to locate the LHC active pace/sense electrode at a desired LHC pace/sense site. The RHC lead is advanced into the RHC chamber to locate RHC active and indifferent pace/sense electrodes therein. Sensing of RHC spontaneous cardiac depolarizations to provide a RHC sense event signal and delivery of RHC pacing pulses is conducted across the RHC active pace/sense electrode and one of the RHC or IPG indifferent pace/sense electrodes. Sensing of LHC spontaneous cardiac depolarizations to provide a LHC sense event signal is conducted across the LHC active pace/sense electrode and one of the RHC active or indifferent pace/sense electrodes or the IPG indifferent can electrode. Delivery of LHC pacing pulses is preferably conducted across the LHC active pace/sense electrode and the RHC indifferent pace/sense electrode, whereby the LHC pacing vector traverses the mass of the LHC.
In a bi-ventricular pacing system, a small diameter, unipolar, left ventricular, coronary sinus (LV CS) endocardial lead and a bipolar right ventricular (RV) endocardial lead are preferably employed to provide the LHC and RHC pace/sense electrodes. In a bi-atrial pacing system, a unipolar, left atrial, coronary sinus (LA CS) lead and a bipolar right atrial (RA) endocardial lead are preferably employed to provide the LHC and RHC pace/sense electrodes. Epicardial leads may be used also, or even bi-polar LV leads or ICD (Implantable CardioDefibrilator) patch electrodes where available and desireable.
The present invention is preferably implemented in pacing systems for providing atrial or ventricular bi-chamber pacing or AV synchronous pacing systems for providing three or four chamber pacing.
The present invention is preferably implemented into an external or implantable pulse generator and lead system selectively employing right and left heart, atrial and/or ventricular leads. The preferred embodiment is implemented in an architecture that allows wide programming flexibility for operating in AV synchronous modes with right and left ventricular pacing or in atrial or ventricular only modes for providing only right and left atrial or ventricular pacing. The AV synchronous embodiments may be implemented into an IPG or external pulse generator and lead system providing right and left ventricular pacing and sensing and either both right and left atrial pacing or just right or left atrial pacing and sensing. Alternatively, the invention can be implemented in IPGs or external pulse generators and lead systems having hard wired connections and operating modes that are not as programmable.